Container-init must behave like global-init to processes within the container and hence it must be immune to unhandled fatal signals from within the container (i.e SIG_DFL signals that terminate the process). But the same container-init must behave like a normal process to processes in ancestor namespaces and so if it receives the same fatal signal from a process in ancestor namespace, the signal must be processed. Further, since processes don't have a valid pid numbers in a descendant pid namespaces, the siginfo->si_pid field must be set to 0. Implementing these semantics requires that send_signal() determine pid namespace of the sender but since signals can originate from workqueues/ interrupt-handlers, determining pid namespace of sender may not always be possible or safe. This patchset implements the design/simplified semantics suggested by Oleg Nesterov. These semantics are: - container-init must never be terminated by a signal from a descendant process. - container-init must never be immune to SIGKILL from an ancestor namespace (so a process in parent namespace must always be able to terminate a descendant container). - container-init may be immune to unhandled fatal signals (like SIGUSR1) even if they are from ancestor namespace (SIGKILL is the only reliable signal from ancestor namespace). Patches in this set: [PATCH 1/5] pid: Implement ns_of_pid [PATCH 2/5] pid: Generalize task_active_pid_ns [PATCH 3/5] Determine if sender is from ancestor ns [PATCH 4/5] Protect cinit from fatal signals [PATCH 5/5] Clear si_pid for signal from ancestor ns TODO: - SIGSTOP and ptrace functionality to be reviewed/fixed. - siginfo->si_pid may need to be cleared in a few more places (eg; __do_notify(), F_SETSIG ?). Limitations/side-effects of current design - Container-init is immune to suicide - kill(getpid(), SIGKILL) is ignored. Use exit() :-) - rt_sigqueueinfo(): siginfo->si_pid value is unreliable/undefined when rt_sigqueueinfo() is used to signal a process in a descendant namespace Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx> _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
